28. Implement strStr()

class Solution {
public:
    int strStr(string haystack, string needle) {
        if(needle==""){
            return 0;
        }
        int k=0,i,j;
        for(i=0;i<haystack.length();i++){
            if(haystack[i]==needle[0]){
                if(i+needle.length()>haystack.length())
                    return -1;
                for(j=i;j<needle.length()+i;j++){
                    if(haystack[j]==needle[k]){
                        k++;
                    }
                }
                if(k==needle.length())
                    return i;
                k=0;
            }
        }
        return -1;
    }
};